1. Field of the Invention
The present invention relates to a method for sorting positive temperature coefficient (PTC) elements having different resistance-temperature characteristics.
2. Description of the Related Art
In general, PTC elements which have positive resistance-temperature characteristics have a characteristic in which the resistance value rapidly increases above the Curie temperature (hereinafter referred to also as CP as appropriate), and are used as, for example, over-current protective elements in electronic circuits or temperature sensing elements.
For these PTC elements, defects in the characteristics caused by, for example, admixture of impurities in a manufacturing process may occur. Therefore, the quality of produced PTC elements should be determined. One example of a method of performing such a determination of the quality is, for example, a method of measuring the impedance of a PTC element and evaluating the quality on the basis of the value of a resistance component (see, for example, Japanese Unexamined Patent Application Publication No. 7-294568 (Patent Document 1). Another example of the determining method is a method of setting the value of an inrush current and the value of a steady-state current during energization and selecting a PTC element having an inrush current and steady-state current that do not exceed a corresponding set value (see, for example, Japanese Unexamined Patent Application Publication No. 9-092504 (Patent Document 2).
Recently, to respond to market demands, PTC elements having various resistance-temperature characteristics are commercially available, and microminiaturization of PTC elements is advancing. Recently, microchip components having a size of, for example, 1.6×0.8 mm and 0.6×0.3 mm, have been developed.
In the course of component management of PTC elements, a PTC element having a different characteristic may be inadvertently mixed with managed PTC elements. In such a case, it is necessary to separate the mixed foreign component. However, it is difficult to separate a PTC element having a different resistance-temperature characteristic by using either of the known methods described above. Thus, an improvement to enhance efficiency in component management is desired.
In order to avoid a foreign component from being mixed, an approach to apply identification marking to PTC elements is available. However, when miniaturization of chips advances, marking a microchip component is difficult, and therefore, it is impossible to distinguish differences in resistance-temperature characteristics from outward appearances. Practically, characteristics cannot be determined by resistance value or resisting pressure that can be measured in a short time. As a result, in order to separate a mixed PTC element, it is necessary to perform a 100-percent inspection and measure the resistance-temperature characteristic of each of the PTC elements, such that a problem arises in which a large amount of time and effort is required.